Why does sugar dissolve better in hot water than in cold water?

When we pour a piece of sugar in his coffee, it quickly dissolves. But when the same piece of sugar is poured into a cold drink, it takes a long time to stir before it finally falls apart. The dissolution of sugar in a solvent is indeed an endothermic process, which requires the supply of heat. However, in a hot liquid, the molecules of water have greater agitation than cold water. They move faster, which induces more frequent collisions with the sugar molecules. These will therefore quickly disintegrate to disperse in water, forming a homogeneous solution.

You can dissolve more sugar in hot water than in cold water.

This is also true for most solid soluble, like salt, which melts faster in a pot of boiling water (although it’s much less obvious than with sugar). By the same process, the‘Hot water also promotes the diffusion of molecules of tea, the latter being therefore quicker to prepare than with cold water. Note that the amount of sugar that can be diluted in water also increases with temperature: at 20°C, it is thus possible to dissolve 2 kg of sugar per liter of water, but you can add up to 4 kg of sugar per liter of water at 90°C.

Gases less soluble in hot water

Conversely, the gas are less soluble in hot water than in cold water. The dissolution of gas in water is exothermic : the gas produces heat when it dissolves, which increases the agitation of the water molecules. As a result, the latter will collide with the gas molecules, which will then disintegrate and escape into theair. This is why soft drinks must be kept in the fridge so that the maximum CO2 stay inside. But it is also a problem for Pisces, which have less oxygen in the water when the ocean warms up.

These are simplified explanations, because in reality many other phenomena come into play, such asentropy some cash. There are also exceptions, such as calcium carbonate and the calcium sulphate, whose solubility decreases with temperature.